Synthetic antibacterial agents such as nalidixic acid and piromidic acid have heretofore been known as therapeutic agents for infective diseases. However, these agents have involved a drawback that they exhibit insufficient effect on intractable diseases such as pyocyanic infection.
Meanwhile, quinolone carboxylic acid derivatives substituted with a fluorine atom at 6 position, such as norfloxacin, ofloxacin, cyprofloxacin and sparfloxacin have been developed and widely used clinically because of their strong antibacterial activities against Gram-negative bacteria.
However, the conventional synthetic antibacterial agents have involved drawbacks in low bioavailability because of their poor absorptivity in a living body, and in low antibacterial activity against Gram-positive bacteria, in particular, tolerant bacteria such as methicillin-resistant Staphylococcus aureus.
Therefore, it is an object of the present invention to provide an antibacterial agent which has strong antibacterial activities against both Gram-negative bacteria and Gram-positive bacteria including tolerant bacteria, and also has superior absorptivity.
In view of the foregoing circumstances, the present inventor has synthesized a great number of quinolone derivatives to investigate their antibacterial activities and absorptivity into the living body. As a result, it has been found that 5-aminoquinolone carboxylic acid derivatives represented by the general formula (1), which will be described subsequently, and salts thereof exhibit extremely enhanced antibacterial activities against Gram-positive bacteria, in particular, tolerant bacteria thereof compared with that of the conventional quinolone carboxylic acid derivatives while retaining good antibacterial activities against Gram-negative bacteria, and also have excellent absorptivity, leading to completion of the present invention.